Heart rhythm disorders are the leading cause of morbidity and mortality in the developed world. Despite a profound difference in physiological mechanisms, anatomic and genetic determinants, and etiology of various arrhythmias, there are only two predominant treatments: electric and ablative therapies. Pharmacological therapy has been mostly ineffective or hampered by side effects. Ablative therapy for atrial tachyarrhythmias is growing in acceptance. However, the ablation procedure is complex, time-consuming, and has a number of side effects. Several modalities of electrotherapy have been effective in preventing sudden cardiac death due to ventricular tachycardia and fibrillation (VT/VF), and in arresting atrial tachycardia and fibrillation (AT/AF). However, the current bioelectric therapy paradigm has a number of limitations. Antitachycardia pacing (ATP) is the most desirable approach due to its low energy requirement, but the efficacy of ATP is limited. High- voltage biphasic shock defibrillation has evolved over the last 70 years as the dominant and highly effective electrotherapy against both AF and VF. However, the energy requirements for AF are suboptimal: high-energy shocks are painful and could cause myocardial damage. In our project we aim to address the limitations of current electrotherapy and present a novel hypothesis: multi-stage phased bioelectric therapy will allow significant reduction in DFT for atrial fibrillaton. Based on previous NIH-funded research from our laboratory we have developed an approach that terminates atrial tachyarrhythmia based on several types of multiple pulse electrotherapies with low, phased (i.e. progressively reducing) energy levels and frequencies: (1) far-field low energy multiple shocks, (2) far-field ultra-low energy entrainment stimulation, and (3) near-field entrainment pacing. We will explore two technological platforms to implement and further investigate our novel method: (1) state-of-the-art lead-based implantable device and (2) flexible electronics developed by the Rogers laboratory at the University of Illinois, Urbana-Champagne. Successful completion of this project will advance implantable bioelectric therapy of cardiac arrhythmias by (1) reducing high-voltage shock induced myocardial damage and post-shock conduction abnormalities secondary to this damage, (2) reducing pain associated with termination of tachyarrhythmias, and (3) reducing energy consumption in the implantable devices. Reduction of the DFT below 0.2J is likely to make implantable atrial defibrillation possible for millions of AF patients. Novel stretchable electronic technology developed by John A. Rogers is likely to transform electrotherapy of cardiac arrhythmias based on high anatomic resolution local sensing and multi-stage therapy of aberrant rhythms.